In communication systems using spread spectrum techniques, the receiver must be rapidly synchronized to the spread spectrum sequence of the incoming signal. A despreading correlator in the receiver must be activated with sufficiently accurate synchronization to the incoming spread signal such that the timing in the receiver can be set for synchronism with the incoming signal. It has heretofore frequently been the practice to achieve synchronization by comparing the incoming spread spectrum sequence to a corresponding stored reference code. The incoming analog signal is sampled and the resulting samples are shifted through a correlator for comparison with a statically stored reference code. A single serial comparison technique of this type is limited in its effectiveness. When a charge transfer device (CTD) is used as the transversal correlator, the length of the correlator is limited by the cumulative effects of charge transfer inefficiency which limits correlator processing gain. The effectiveness of serial correlation is also limited by data or frequency offsets which effectively limit the useful correlator length.
In view of the limitations in conventional practice for detecting a spread spectrum signal to achieve synchronization, there exists a need for a method and apparatus for correlating an incoming spread spectrum signal with a stored reference code such that substantial correlator lengths can be achieved with such lengths preferably being in excess of one data bit long.